The roller thrust bearing (including the needle roller thrust bearing) such as disclosed in JP8-109925(A) is mounted in a rotating section of the transmissions or the like. The roller thrust bearing supports thrust loads that are applied to the rotating section. In this roller thrust bearing, the side surface in the axial direction of a pair of members rotating relative to each other may be used as is as the thrust raceway. However, when one or both of the members of this rotating section are made using a material for which it is difficult to maintain the necessary hardness, or, when it is difficult or troublesome to process the members to give the required smoothness to the surface, a roller thrust bearing that has one or two races assembled in the roller thrust bearing is used.
FIG. 10 and FIG. 11 illustrate an example of a roller thrust bearing with races. This roller thrust bearing 1 comprises a plurality of rollers 2 (including needles) that are arranged in a radial direction, a cage that holds these rollers 2, and a pair of thrust races 4a, 4b that hold these rollers 2 from both sides. The cage 3 is composed of a combination of a first cage element 5 and a second cage element 6 that are both formed into an annular disk shape having a U-shaped cross section, the combination having a hollow circular ring shape, and as illustrated in FIG. 11, has the same number of pockets 7 as the number of rollers 2 that are arranged radially.
The first cage element 5 is formed so that by performing plastic working such as pressing of a metal plate such as steel plate, a first inner-diameter side cylindrical section 9 and a first outer-diameter side cylindrical section 10 that extend in the axial direction are respectively connected to the inner circumferential edge and outer circumferential edge of a first annular disk section 8 that extends in the radial direction such that they are concentric. First through holes 11 that are long in the radial direction and rectangular for forming pockets 7 are formed at a plurality of locations in the circumferential direction of the first annular disk section 8. The second cage element 6 as well is formed such that by performing plastic working such as pressing of a metal plate such as steel plate, a second inner-diameter side cylindrical section 13 and a second outer-diameter side cylindrical section 14 that extend in the axial direction are respectively connected to the inner circumferential edge and outer circumferential edge of a second annular disk section 12 that extends in the radial direction such that they are concentric. Second through holes 15 that are long in the radial direction and rectangular for forming pockets 7 are formed at a plurality of locations in the circumferential direction of the second annular disk section 12. The first cage element 5 and the second cage element 6, with the first through holes 11 and the second through holes 15 aligned with each other in the axial direction, fit together such that the second outer-diameter side cylindrical section 14 fits inside the inner-diameter side of the first outer-diameter side cylindrical section 10, and the second inner-diameter side cylindrical section 13 fits around the outer-diameter side of the first inner-diameter side cylindrical section 9. Then, by bending the tip end edge of the first inner-diameter side cylindrical section 9 outward in the radial direction, the first cage element 5 and the second cage element 6 are prevented from coming apart from each other.
The thrust races 4a, 4b are both formed into an annular disk shape using a metal plate having sufficient hardness. Short cylindrical shaped flange sections 16a, 16b are formed around the inner circumferential edge of the one thrust race 4a that is typically called the inner ring (left race in FIG. 10), and around the outer circumferential edge of the other thrust race 4b that is typically called the outer ring (right race in FIG. 10). A plurality of locations on the tip end section of the flange section 16a located on the inside in the radial direction are bent outward in the radial direction, and a plurality of locations on the tip end section of the flange section 16b located on the outside in the radial direction are bent inward in the radial direction forming fastening sections 17a, 17b. These fastening sections 17a, 17b engage with the inner circumferential edge or outer circumferential edge of the cage 3, connecting the component parts of the roller thrust bearing 1 together so that do not come apart.
As illustrated in FIG. 10, a roller thrust bearing 1 that is constructed in this way is mounted in this rotating section by fitting the flange section 16b that is formed around the outer circumferential edge of the thrust race 4b inside a circular concave shaped supporting section 19 that is formed in the casing 18 and that is one member of the rotating section. In this state, the right surface of the thrust race 4b comes in contact with the rear surface 19a of the support section 19, and the left surface of the other thrust race 4a comes in contact with the end surface 20a of the opposing member 20 such as the rotating shaft, which is the other member of the rotating section. As a result, this opposing member 20 is supported so as to be able to rotate freely with respect to the casing 18, and a thrust load that acts between these members 18, 20 is supported. It is also possible for the rear surface 19a of the support section 19 of the casing 18 or the end surface 20a of the opposing member 20 to be used as the raceway, and to omit one or both of the thrust races 4a 4b. 
When using this kind of roller thrust bearing 1, a force is applied to the rollers 2 in the radial direction of the cage 3 due to centrifugal force. This force presses the outer-diameter side end surfaces 21 of both the axial end surfaces of the rollers 2, which are located on the outside in the radial direction of the cage 3, against the outer-diameter side circumferential edge sections 22a, 22b of the circumferential edge sections of the first through holes 11 and second through holes 15 that form the pockets 7, which are located on the outside in the radial direction of the cage 3. However, the outer-diameter side end surfaces 21 are not necessarily pressed evenly against the outer-diameter side circumferential edge sections 22a, 22b. Actually, due to errors in manufacturing and displacement in the axial direction (left to right direction in FIG. 10) of the cage 3, the outer-diameter side end surfaces 21 are pressed against one of the outer-diameter side circumferential edge sections 22a, 22b, and the surfaces come in sliding contact with each other.
The surface pressure (P) at the area of sliding contact increases as the rotational speed of the roller thrust bearing 1 during use becomes faster and the centrifugal force becomes greater. Moreover, the area of sliding contact is located at a position that is separated from the center axis line of the rollers 2, so the sliding speed (V) between one of the outer-diameter side circumferential edges 22a, 22b and the outer-diameter side end surface 21 at the area of sliding contact becomes faster to some extent. In this way, the PV value, which is the product of the surface pressure (P) and the sliding speed (V) at the area of sliding contact and is widely known as a parameter that indicates the effect on wear, becomes large. As a result, depressions may be formed on one of the outer-diameter side circumferential edge sections 22a, 22b due to wear. As such depressions becomes large, the rollers 2 that are held in the pockets 7 slide to the rear sides of the first annular disk section 8 or second annular disk section 12 where these depressions are formed, and the rollers 2 are not able to roll smoothly. At the same time, the surface on the right side of the first cage element 5 is pressed against the side surface of the thrust race 4b, or the surface on the left side of the second cage element 6 is pressed against the side surface of the thrust race 4a, and the resistance to the cage 3 rotating relative to one of the thrust races 4a, 4b becomes large. As a result, not only does the efficiency of the mechanical device such as a transmission in which the roller thrust bearing 1 is assembled worsen, in extreme cases, there is a possibility that the mechanical device will not operate properly due to damage such as seizure.
As performance of recent automobiles improves, and the rotation speed of rotating sections such as a transmission becomes faster, wear that causes this kind of problem occurs more readily than in the past. Moreover, this kind of wear occurs more easily the greater the amount of displacement of the rollers 2 is inside the pockets 7. The displacement amount that the rollers 2 that are held inside the pockets 7 of the cage 3 displace in the axial direction (left-right direction in FIG. 10) becomes greater the larger the space is between the rolling surfaces of the rollers 2 and the inner circumferential edge of the pockets 7. In pockets 7 that allow the rollers 2 to displace a large amount, the rollers 2 easily displace, and the center of rotation of the rollers 2 no longer coincides with the radial direction of the cage 3, so it becomes easy for so-called skewing to occur. When skewing occurs, a component in the radial direction of the cage 3 occurs according to the direction of movement of the rollers 2 as the rollers 2 rotate. It is thought that when this component in the radial direction is toward the outside in the radial direction of the cage 3, the surface pressure (P) of the areas of sliding contact between the outer-diameter side end surface 21 and the outer-diameter side circumferential edge sections 22a, 22b becomes high together with the force due to centrifugal force, and wear occurs more easily.
JP2003-172346(A) discloses construction of a roller thrust bearing wherein on the outer-diameter side end section of the cage, metal plates form a pair of cage elements that overlap in the center section in the axial direction of the cage. With this construction, it is considered to be possible to prevent rollers from slipping into depressions due to the kind of wear described above. However, with this construction, the surface areas of the outer circumferential surface of the cage become small, and there is a possibility that the opposing surface that faces this outer circumferential surface will wear due to friction with this outer circumferential surface, so the sites where this construction can be applied are limited. Moreover, it is necessary to spot weld the location where the metal plates overlap, and because the construction differs greatly from the conventional construction, conventional equipment cannot be used, and therefore there is a possibility that the manufacturing cost will increase.
JP2002-206525(A) discloses construction of a roller thrust bearing that comprises a cage having a sheet of metal plate that are formed into a wave shape in cross section. With this construction, by adequately devising the location where to form the pockets, it is considered to be possible to prevent the roller from slipping into depressions due to wear such as described above. However, this construction as well, greatly differs from conventional construction, so it is not possible to obtain the effect of preventing the kind of wear described above using conventional equipment.
In regards to this, JP2005-164023(A) discloses a roller thrust bearing 1a having construction as illustrated in FIGS. 12A and 12B, with the object of preventing a reduction of dynamic torque and abnormal wear of the cage. The cage 3a of this improved roller thrust bearing 1a is also formed by combining a first cage element 5a and second cage element 6a into a hollow circular ring shape, and the same number of pockets 7 as rollers 2a are arranged in a radial fashion around the center of the cage 3a. In the radial direction of the cage 3a, both the outer-diameter side end surface 21a and the inner-diameter side end surface 23 of the rollers 2a are partial spherical surfaces having a center of curvature on the center axis of the rollers 2a, and the center sections of these surfaces protrude the most in the axial direction.
In the cage 3a of this improved roller thrust bearing 1a, in order to form pockets 7a, first through holes 11a are formed in a first annular disk section 8a of the first cage element 5a, and second through holes 15a are formed in a second annular disk section 12a of the second cage element 6a. Particularly, the second through holes 15a are open to the outer circumferential edge of the second annular disk section 12a. Then, with the rollers 2a held in the pockets 7a displaced as far as possible to the outside in the radial direction of the cage 3a, the center section of the outer-diameter side end surface 21a and the inner circumferential surface of the second outer-diameter side cylindrical section 14a of the second cage element 6a come in contact in the contact section 24 indicated by the small dashed-line circle mark in FIG. 12B. The sliding speed (V) of the center section that corresponds with the contact section 24 is low, so the PV value at the contact section 24 is kept low, and the friction resistance and wear at the contact section between the center section of the outer-diameter side end surface 21a and the inner circumferential surface of the second outer-diameter side cylindrical section 14a are kept negligible. This improved roller thrust bearing 1a is advantageous from the aspect of reducing the rotation resistance (dynamic torque) and improvement of durability, however, when a roller thrust bearing with races is constructed using a combination of this construction and thrust races, there is room for improvement when considering preventing the cage 3a from coming apart from the thrust race 4b, and maintaining smooth, relative rotation between the cage 3a and the thrust race 4b. 
FIG. 13 illustrates simple combined construction of combining an improved roller thrust bearing 1a having construction similar to that illustrated in FIG. 12 with the thrust race 4b illustrated in FIG. 10. In this construction, the first annular disk section 8b of the first cage element 5b of the roller thrust bearing 1b faces the race section 25 of the thrust race 4b. In order to prevent the thrust race 4b from coming apart from the cage 3b, the plurality of fastening sections 17b that are formed on the flange section 16b of the thrust race 4b are located further on the opposite side in the axial direction from the race section 25 than the tip end edge of the first outer-diameter side cylindrical section 10b of the first cage element 5b. Furthermore, the protruding amount (L) that each of the fastening sections 17b protrudes from the inner circumferential surface of the flange section 16b is less than the thickness (T1) of the first outer-diameter side cylindrical section 10b (L<T1).
In the case of this construction, as long as the thickness (T1) of the first outer-diameter side cylindrical section 10b is sufficiently large, it is possible to maintain the protruding amount (L) of the fastening sections 17b, and thus it is possible to sufficiently maintain the engagement amount (amount of overlap in the radial direction) of the fastening sections 17b and the tip end section of the first outer-diameter side cylindrical section 10b of the cage 3b, and it is possible prevent the thrust race 4b from coming apart from the cage 3b. However, in this roller thrust bearing 1b, the thicknesses of the metal plates of the pair of cage elements 5a, 6b of the cage 3b are the same as each other, so it depending on the size of the roller thrust bearing with races, and particularly depending thickness dimension in the axial direction, it becomes difficult to maintain the thickness of the first outer-diameter side cylindrical section 10b while at the same time maintain the strength and rigidity of the cage 3b. 
For example, the problem becomes very evident when the thickness in the axial direction of the overall roller thrust bearing with races, which is the total of the thickness of the thrust race 4b and the diameter of the roller 2a, is 2.5 to 6 mm. In other words, when taking into consideration maintaining strength and rigidity of the cage when this thickness in the axial direction is 6 mm or less, the thickness of the first outer-diameter side cylindrical section 10b becomes fairly small, and the engagement amount of the fastening sections 17b and the tip end section of the first outer-diameter side cylindrical section 10b becomes too small, so it becomes uncertain whether the thrust race 4b and cage 3b can be kept from coming apart. When the thickness in the axial direction is less than 2.5 mm, the thickness dimensions of all parts become too small, so an applicable roller thrust bearing with races cannot be achieved.
As illustrated in FIG. 14, by making the protruding amount of the fastening sections 17c large regardless of the thickness of the first outer-diameter side cylindrical section 10b, it is possible to prevent the thrust race 4b from coming apart from the cage 3b, however, instead, the tip end sections of the fastening sections 17c interfere with the outer circumferential edge section of the second cage element 6b. The outer circumferential edge section of the second cage element 6b is gear shaped (concavo-convex shaped) due to the end sections of the second through holes 15b that are uniformly spaced in the circumferential direction. Therefore, not only does severe vibration occur due to the interference in this area, but also rotation resistance and wear become extreme.
By forming an engagement section for preventing separation from the cage by bending the tip end section of the flange section of the thrust race around the entire circumference, the edge on the end of this engagement section is smooth in the circumferential direction. However, when an error is made in the assembly direction of the thrust bearing with a race, a problem occurs in that durability is lost due to insufficient lubrication, so in order to prevent reverse assembly in which this problems occurs, it is necessary to provide a plurality of protruding sections for preventing reverse assembly that protrude outward in the radial direction on the tip end edge of the flange section of the thrust race; however, in this construction, it is not possible to form such protrusions for preventing reverse assembly. Therefore, as construction for preventing reverse assembly, construction in which the outer diameter of the thrust race 4a (see FIG. 10) is greater than the outer diameter of the thrust race 4b and the inner diameter of the supporting section 19 of the casing 18 is possible. However, in this construction, due to the outer diameter of the thrust race 4a becoming large, there are disadvantages such as the weight of the thrust race 4a increasing, construction of the assembly section being limited, the flow path area for the lubrication being narrow, and the like.
Furthermore, the roller thrust bearing 1, and the roller thrust bearing with races having a combined pair of thrust races 4a, 4b may be applied to an application such as when the relative eccentricity between the two members that are composed of a rotating section and support the thrust bearing with races becomes large. In this case, when this amount of relative eccentricity is greater than the space inside the bearing, or in other words, the space between the outer circumferential surface of the first outer-diameter side cylindrical section 10 of the first cage element 5 and the inner circumferential surface of the flange section 16b of the thrust race 4b, or the space between the inner circumferential surface of the first inner-diameter side cylindrical section 9 of the first cage element 5 and the outer circumferential surface of the flange section 16a of the thrust race 4a, interference occurs between the one of the thrust races 4a, 4b and the first cage element 5, and due to this interference, there is a problem with wear occurring in the first cage element 5. The edge on the tip end of the first inner-diameter side cylindrical section 9 of the first cage element 5 is crimped and fastened to the second inner-diameter side cylindrical section 13 of the second cage element 6, however, the tip end edge of the first outer-diameter side cylindrical section 10 of the first cage element 5 is not crimped, and there is a possibility that a small space will occur between that edge and the second outer-diameter side cylindrical section 14 of the second cage element 6. In this case, contact between the first outer-diameter side cylindrical section 10 and the thrust race 4b will cause bending to occur in the first outer-diameter side cylindrical section 10, and the round section on the inside of the connecting section between the first annular disk section 5 and the first outer-diameter side cylindrical section 10 becomes an area of concentrated stress, and thus there is a possibility that cracking will occur in the first cage element 5.